The present invention relates to elastic films having both water-vapor-permeability and waterproofness, and provides novel products having, simultaneously, water-vapor-permeable and waterproofness properties.
In various clothing apparel, tents and other articles, materials having waterproof characteristics and water-vapor-permeability have been put to practical use in recent years and have been utilized as comfortable outdoor wear and the like. However, many of these materials lack elasticity or are at most slightly elastic. Materials having high elasticity are known, but such known materials are generally poor in water-vapor-permeability and most are not substantially waterproof.
Materials having both waterproof and water-vapor-permeable properties are known, such as expanded porous materials of polytetrafluoroethylene (hereafter referred to as PTFE) disclosed in, for example, U.S. Pat. No. 3,953,566. This expanded PTFE is both highly porous and has high crystallinity. The highly stretched finished materials possess a high degree of fibrillation, as well as the aforesaid waterproofness and water-vapor-permeable properties.
For waterproof, water-vapor-permeable materials which lack elasticity as mentioned above, for example, in sporting apparel, those having a size large enough to ensure stretching of the wearer's body can be provided; on the other hand, apparel of such a large size becomes loose, and detracts from the beauty of the garments when they are worn. Particularly in sports requiring speed, wind resistance and the like increases and detracts from the usefulness of the garment. The above-mentioned, expanded PTFE materials are excellent in planar tensile strength, as a result of fibrillation to a high degree, but they possess poor strength in the thickness, or Z- direction. Particularly in unsintered, expanded PTFE, a peel-off phenomenon of the surface layer, which is called fracture, can occur. In order to avoid such a phenomenon, sintering may be required but sintered PTFE causes fusion between fibrils so that elasticity of the film becomes poor because of no lubrication between fibrils. Accordingly, even though such sintered, expanded PTFE can be used and laminated to other materials, elasticity of the partner laminate is inhibited by the aforesaid sintered PTFE, and substantial elasticity is not obtained for the laminate as a whole.
U.S. Pat. No. 4,443,511 provides a waterproof and breathable elastomeric polytetrafluoroethylene layered article for use in, for example, material for protective articles. The waterproof and breathable polytetrafluoroethylene layered article can for example, exhibit elastomeric properties of stretch to break of 275% in the machine direction, and 145% in the transverse direction and a total stretch recovery of at least 39% after being stretched to 75% extension for 100 cycles. That invention further provided a waterproof and breathable elastomeric polytetrafluoroethylene layered article bonded to a stretch fabric. The waterproof and breathable elastomeric polytetrafluoroethylene layered article bonded to a stretch fabric is durable and possesses a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day, and preferably above the 2000 gms/m.sup.2 day.
U.S. Pat. No. 4,194,041 discloses a waterproof and breathable polytetrafluoroethylene (PTFE) laminate that possesses a high moisture vapor transmission rate under adverse climatic conditions. Such laminates and modified forms thereof are commercially available from W. L. Gore & Associates, Inc. The waterproof and breathable laminate of U.S. Pat. No. 4,194,041 comprises a flexible first layer of a microporous hydrophobic material having a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day, an advancing water contact angle exceeding 90 degrees and a second layer of continuous hydrophilic elastomeric material attached to the inner face of the first layer whereby the second layer has a moisture vapor transmission rate exceeding 1000 gms/m.sup.2 day and does not permit the detectable passage of liquid water therethrough at hydrostatic pressures of about 24 cm water head and about 172 KN/m.sup.2 for 30 seconds.
The porous membrane of expanded polytetrafluoroethylene (PTFE) used in the above laminate can be provided by following the techniques of U.S. Pat. No. 3,953,566. Such membranes and modified forms thereof are commercially available under the registered trademark GORE-TEX.RTM., sold by W. L. Gore & Associates, Inc. These expanded, porous PTFE membranes satisfy the requirements of being waterproof while also being permeable to the flow of water vapor. The expanded porous PTFE membranes are inherently hydrophobic and contain very small pores that resist the entry of liquid water even at substantial pressures or when rubbed or flexed, but readily allow the flow of gases including water vapor. Unlike wicking materials breathability is achieved by evaporation of liquid water inside the garment or on the inner surface of the membrane followed by gaseous flow or diffusion of water vapor through the membrane to the outside. The teachings of that patent are incorporated herein by reference.
U.S. patent application Ser. No. 443,139, filed Nov. 19, 1982, now abandoned describes a waterproof and breathable elastomeric polytetrafluoroethylene layered article for use in, for example, material for footwear articles. The waterproof and breathable polytetrafluoroethylene layered article can, for example, exhibit elastomeric properties of stretch to break of 275% in the machine direction, and 145% in the transverse direction and a total stretch recovery of at least 39% after being stretched to 75% extension for 100 cycles.
U.S. patent application Ser. No. 603,186, filed Apr. 23, 1984 discloses certain polyurethanes impregnated to an extent into expanded, unsintered PTFE sheets.